In general, in a liquid crystal display device which performs color display, one pixel is divided into three sub-pixels of a red color pixel in which a color filter that transmits red color light is provided, a green color pixel in which a color filter that transmits green color light is provided, and a blue color pixel in which a color filter which transmits blue color light is provided. The color display is enabled by color filters provided in these three sub-pixels, but about two thirds of backlight light which is irradiated to a liquid crystal panel is absorbed by the color filters. Therefore, a liquid crystal display device of a color filter system has a problem that light use efficiency is low. Thus, a liquid crystal display device which adopts field-sequential driving that performs color display without using the color filters is being focused.
In a general liquid crystal display device which adopts the field-sequential driving, a display period of one screen (one frame period) is divided into three fields (first to third fields). Note that, although the field is also referred to as a sub-frame, the term of the field is consistently used in the following description. For example, a red color screen is displayed based on a red color component of an input signal in the first field, a green color screen is displayed based on a green color component of the input signal in the second field, and a blue color screen is displayed based on a blue color component of the input signal in the third field. By displaying the primary colors one by one as described above, a color image is displayed in a liquid crystal panel. Because display of the color image is performed in this manner, a color filter is unnecessary in the liquid crystal display device that adopts the field-sequential driving. Thereby, light use efficiency in the liquid crystal display device which adopts the field-sequential driving becomes about three times compared with the liquid crystal display device of the color filter system.
Meanwhile, in a liquid crystal display device of an active matrix type, generally, a plurality of gate bus lines (scanning signal lines) provided in a liquid crystal panel are driven one by one sequentially. Therefore, writing (charging) of a pixel on an upper part of a panel to a pixel capacitance is performed near a start of each field, writing (charging) of a pixel on a center part of the panel to the pixel capacitance is performed about in the middle of each field, and writing (charging) of a pixel on a lower part of the panel to the pixel capacitance is performed near an end of each field. Accordingly, when the field-sequential driving is adopted, it is necessary to cause a backlight to emit light in synchronization with scanning being performed sequentially from the upper part of the panel to the lower part of the panel. Note that, the processing for causing the backlight to emit light sequentially from the upper part of the panel to the lower part of the panel is referred to as “backlight scanning” below.
An invention of a display device that performs backlight scanning is disclosed, for example, in following literatures. Japanese Unexamined Patent Application Publication No. 2012-109227 discloses an invention of a display device that performs backlight scanning by using a direct-type backlight. Further, Japanese Unexamined Patent Application Publication No. 2012-119311 discloses an invention of a display device that performs backlight scanning by using an edge-light type (side-light type) backlight.